The present invention relates to an apparatus and method for detecting movement of a vessel on a cooktop surface and more particularly to the detection of movement by measuring signals produced by an inductive loop positioned below the cooktop surface.
A popular trend in electronically controlled cooktops and/or ranges, typically, includes a cooktop surface composed of a glass-ceramic material that is positioned above one or more radiant heating elements. The cooktop includes various user controls that can be used by an operator to adjust the amount of power supplied to the radiant heating elements and, therefore, the heat desired for cooking. The radiant heating elements can be powered by, for example, electricity, natural gas, propane or iso-butane. The radiant heating elements and the controls are connected to a controller that user controls the amount of energy supplied to the cooktop. The cooktop can also includes temperature sensors and/or other sensor that are connected to the controller to aid in controlling the energy supplied to the radiant heating element and ultimately the heat supplied to the cooktop. The temperature sensors and other sensors are also used in conjunction with the controller and/or other processors to detect certain detrimental conditions that can arise during operation of the cooktop.
For example, the temperature sensors in conjunction with the controller and/or other processors can detect a boil dry condition. Typically, a boil dry condition occurs when the liquid contents of a vessel positioned on the cooktop is caused to boil by heat from the radiant heating source such that all the liquid contents are boiled from the vessel. Specifically, a boil drying condition is predicted when a relatively rapid increase in the temperature of the cooktop surface occurs while constant energy is being supplied to the radiant heating element. When all the liquid contents have been evaporated and/or converted to gas from the vessel being heated on the cooktop, the radiant heating source will continue to supply heat to the cooktop causing the cooktop surface and/or the vessel to overheat and possibly become damaged. To prevent such damage, the temperature sensors and/or other sensors provide information to the controller and/or other processors that predicts the boil dry condition based on specific sensor characteristics, and when a boil dry condition is detected, energy is no longer supplied to the radiant heating element.
In addition, the controller is programmed with a maximum temperature that should not be exceeded to ensure a long service life for the glass ceramic cooktop surface. When the temperature sensors and controller determine that the temperature of the cooktop and/or the vessel is approaching the maximum temperature, the controller instructs the radiant heating source to reduce the heat being applied to the cooktop such that a constant temperature is maintained. The controller also ensures that the constant temperature is at or below the maximum temperature. When the controller holds the radiant heating element at a constant temperature, the controller enters a condition known as thermal limiter mode. While in thermal limiter mode, the temperature of the cooking surface and/or the vessel cannot be used to determine if a boil dry condition has occurred because the cooktop and/or range is being held at a constant temperature. Therefore when the controller is in thermal limiter mode, a boil dry condition is determined by monitoring the energy being applied to the radiant heating source. During thermal limiter mode, a rapid decrease in energy applied to the radiant heating source to maintain the maximum temperature will be interpreted as a boil dry condition by the controller, and energy will no longer be applied to the radiant heating element.
When the controller is in thermal limiter mode, conditions may occur that make the controller predict a false boil dry condition. If the bottom of the vessel has areas that are warped, dirty or imperfect, the thermal characteristics of the vessel can change as the vessel is, for example, moved on the cooktop surface. These thermal characteristics can cause changes in the temperature sensed by the temperature sensor when the vessel is moved or rotated on the cooktop, when the vessel is heated or cooled, or when cold or hot contents are added to the vessel. For example, the temperature sensor may be located near an area where the bottom of the vessel has good thermal contact, and then the vessel is moved or rotated such that an area having poor thermal contact is located near the temperature sensor. Under these conditions, the temperature sensed by the temperature sensor may increase simply because the vessel has been moved or rotated. Due to the increase in temperature sensed by the temperature sensor, the controller may instruct that less energy should be applied to the radiant heating element to maintain the constant temperature. Thus, since less energy is being applied to the radiant heating source to maintain the temperature, the controller may detect a false boil dry condition during thermal limiter mode. However, under the condition where the change in temperature is caused by a warped vessel, a boil dry condition may not necessarily exist because the poor thermal characteristics of the vessel caused the change in temperature rather than an actual boil dry condition. The false boil dry condition can cause dissatisfaction to an operator of the cooktop because when a boil dry condition is detected the power to the radiant heating element is turned off. Therefore, a desire exists to eliminate or reduce false detection of boil dry conditions resulting from vessels having poor thermal qualities in an electronically controlled cooktop.
In one exemplary embodiment, an apparatus is provided for detecting movement of a vessel positioned on a cooktop surface. The apparatus comprises a radiant heating element positioned below the cooktop surface for heating at least the vessel. A controller is provided and is connected to the radiant heating element. The controller controls power supplied to the radiant heating element. A temperature sensor is connected to the controller and measures the temperature near the cooktop surface. An inductive loop is positioned proximate to the cooktop surface. A detection circuit is connected to the controller and the inductive loop. The detection circuit detects movement of the vessel on the cooktop surface using signals produced by at least the inductive loop.
In even another exemplary embodiment, a method is provided for detecting movement of a vessel on a cooktop surface. The movement is detected using a resonant circuit including an inductive loop. The method comprising supplying an energy signal to the inductive loop. At least a resultant signal produced by the inductive loop is measured. At least a magnitude and phase of angle of the resultant signal are determined. An instantaneous inductance of the inductive loop is calculated from at least the magnitude and the phase angle of the resultant signal. A reference inductance is determined. The reference inductance is determined by tabulating a predetermined number of instantaneous inductances over a predetermined amount of time, and calculating the reference inductance from the tabulated instantaneous inductances. Movement of the vessel is detected by comparing the instantaneous inductance to the reference inductance.